Prisms for combining light in projection systems have illumination and off-state light paths internal to prism, as well as total internal reflection (“TIR”) surfaces. Also, current off-state light hits the sides of the prisms. These three scatter sources increase the chance of light scatter and therefore reduce the upper limit of contrast ratio of projector systems. While dichroic plates could be used in place of the prisms, the dichroic plates need to be very thin, as well as optically flat, so they do not introduce optical aberrations to the projection optical path.